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Old 04-12-2009, 09:21 PM   #1
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"C" wire installation


I have a GMP100-4 furnace unit and just got a thermostat to replace a very old inefficient one. The problem is that the new thermostat requires a "C" wire connection, apparently to power the unit (no battery option). Is there a simple fix for this? Can include pics of furnace board if it would help.

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Old 04-12-2009, 09:28 PM   #2
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"C" wire installation


The r wire is always hot.


Last edited by kenmac; 04-12-2009 at 10:47 PM.
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Old 04-12-2009, 10:16 PM   #3
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"C" wire installation


R=power +
C=power -

Depending which series board you have.
You'll need to wire directly to the transformer common.
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Old 04-12-2009, 10:21 PM   #4
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"C" wire installation


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Old 04-12-2009, 10:41 PM   #5
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"C" wire installation


The C teminal of the stat connects to the C terminal of the board, or transformer.

Its the same as an A/C condenser needing to be connected to the C terminal of the board or transformer.

You may be thinking of jumping the RC and RH terminals together.
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Old 04-12-2009, 10:45 PM   #6
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"C" wire installation


been , You got it.. Just looked at mine.. That's exactly what I was thinking.. I deleted the other so he wouldn't get confused.... Thanks been
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Old 04-13-2009, 01:15 PM   #7
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"C" wire installation


If it needs a C wire then another wire would have to be run to the tstat from the furnace ( a huge pain). I would return the tstat and buy a Honeywell Vision or FocusPro as they are battery operated and very good. I saw a very slim Robertshaw type w/o battery and after a power shutdown it was very slow/weird on startup. Did not impress me.
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Old 04-13-2009, 01:48 PM   #8
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"C" wire installation


There is a priduct called "Add a wire" which can "make" an extra wire for you. Probably difficult for a DIY.
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Old 04-13-2009, 02:04 PM   #9
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"C" wire installation


Based on my experience those are ABSOLUTELY horrible/unreliable and I hate them. When they go haywire/on the fritz they can damage a circuit board etc. Stay away from them if at all possible or you may be sorry.
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Old 04-13-2009, 05:00 PM   #10
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"C" wire installation


I have actually run a wire from the furnace to the thermostat, but simply don't know where to connect to the furnace board. Thermostat that my wife purchased has a remote (she wants that). Are there any battery powered models that don't require the C hook up? Thanks for all of the responses. Again, I can provide a pic of the board if that would help.
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Old 04-13-2009, 05:34 PM   #11
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"C" wire installation


Quote:
Originally Posted by yuri View Post
Based on my experience those are ABSOLUTELY horrible/unreliable and I hate them. When they go haywire/on the fritz they can damage a circuit board etc. Stay away from them if at all possible or you may be sorry.
Hey Yuri, you mean the "Priduct"? Yeah I hate that too when they fail.

Which Priduct do you hate more the Honycomb brand or the Black Dodgers
brand
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Old 04-13-2009, 05:38 PM   #12
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"C" wire installation


You can provide a pic. Some of the Goodmans I ran into don't have a C terminal. You have to trace the leads from the 24v transformer and use wire connectors. The 2 Honeywells I recommended are the best I know of and available at HDepot. I recommend the Honeywell as I am a tech and have seen lots of poor quality thermostats do weird things and can sometimes damage a circuit board. Those 2 require no C wire/terminal.

Last edited by yuri; 04-13-2009 at 05:50 PM.
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Old 04-13-2009, 05:39 PM   #13
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"C" wire installation


It has a remote control?

Or a remote sensor?
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Old 04-13-2009, 05:40 PM   #14
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"C" wire installation


Clover, We have had terrible results with fastst*ts. Had one turn a A/C contactor into a machine gun.
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Old 04-13-2009, 06:08 PM   #15
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Clover, We have had terrible results with fastst*ts. Had one turn a A/C contactor into a machine gun.


LOL...what caliber was it firing?

Chattering like an SOB I bet. Never tried the product, din't need it or trust it.

I have yet to not be able to get cable to a furnace, and i consider myself quit fortunate for it.

Honeywell has their IAQ stat and there are several wireless product on the market.

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